*2.2.2. Cytotoxicity assay*

Cells were seeded into a 6 well plate and allowed to grow for 48 h. The cells were treated for 24 h with 1-25 uM of sodium chromate or 0.05-10 ug/cm2 lead chromate. After 24 h we harvested the cells using a standard protocol [7]. Briefly, cells were harvested, counted and re-plated into 100 mm dishes at colony forming density, allowed to grow approximately 2 weeks, then stained and counted. Treated dishes were compared to the untreated control.
